74 EFFECT OF POWDERED EGG YOLK IN THE EXTENDER AND DONOR AGE ON FRESH AND THAWED SPERM MORPHOMETRY IN SMALL RUMINANTS

Abstract

Our aim was to reduce heterogeneity and microbiological contamination risk on small ruminant semen cryopreservation by replacement of fresh egg yolk by pasteurized powdered egg yolk, assessing simultaneously the effect of the donor age (1 year v. 2 years old) on sperm head morphometry of fresh and thawed sperm. Briefly, fresh ejaculates from 8 rams and from 8 bucks were collected in autumn during 2 consecutive years. Immediately after collection, ejaculates from each species were mixed in equal quantities, and pooled semen was centrifuged twice (600 g for 10 min). Then the pellet was split into 2 aliquots and resuspended in an extender containing 15% (v/v) of fresh or powdered egg yolk supplemented with 5% glycerol in a Tris-based medium. Afterward, sperm samples were refrigerated at 5°C for 4 h before being frozen in nitrogen liquid vapours. Buck and ram sperm-head morphometry was analysed by computer-assisted sperm analysis (ISAS®) on fresh and thawed sperm previously stained with Diff Quick®, and the data were analysed using ANOVA (mean ± s.e., n = 6). From ram sperm studies, no differences were found between fresh and post-thaw sperm, neither between egg yolk-based extenders or donor ages, showing the following mean values of head length (8.4 ± 0.0 μm), width (4.9 ± 0.0 μm), area (34.2 ± 0.1 μm²), perimeter (23.4 ± 0.1 μm), ellipticity (1.7 ± 0.0), elongation (0.2 ± 0.0), rugosity (0.8 ± 0.0), and regularity (0.9 ± 0.0). Likewise buck semen did not show significant differences on sperm-head dimensions after cryopreservation, only on head-shape parameters as ellipticity, elongation, and regularity between fresh and thawed sperm from 2-year-old donors, independently of egg yolk used as cryoprotectant. However, the age of the buck had a significant effect on all assessed morphometric parameters in fresh and thawed sperms, except regularity (Table 1). Our results suggest that, from a morphometric point of view, the powdered egg yolk can be used satisfactory on small ruminant sperm cryopreservation, but in goats, the head changes due to the donor age should be considered.

Table 1.  Effect of fresh v. powdered egg yolk (EY) in the extender and donor age on fresh and thawed buck-sperm morphometry

Research supported by INIA (RZ2009–00008–00–00), Generalitat de Catalunya (2009SGR0621 and CUR-DIUE), and FSE and Fundación Carolina.